Electrolytic process for slating a curvilinear aluminum workpiece

ABSTRACT

A process for slating a curvilinear workpiece by electrolytically depositing aluminum oxide on the surface of the workpiece using a temperature controlled sulfuric acid bath containing a high concentration of aluminum. The process produces a craze-free, slightly abrasive surface useful for erasably receiving chalk marks. This process is particularly useful in forming world globes which may be used with chalk for educational and illustrative purposes and then easily erased.

United States Patent [1 1 Woods 7 [451 Nov. 13, 1973 1 ELECTROLYTIC PROCESS FOR SLATING A CURVILINEAR ALUMINUM WORKPIECE [75] Inventor: Jack L. Woods, Ogden, Utah [73] Assignee: Puma-Technological Industries,

Inc., Salt Lake City, Utah [22] Filed: July 21, 1972 [21] Appl. No.: 274,017

[52] US. Cl. 204/33, 204/58 [51] Int. Cl C23b 9/02 [58] Field of Search 204/33, 58, 35 N [56] References Cited UNITED STATES PATENTS 3,672,972 6/1972 Dorsey 204/58 3,616,308 10/1971 Cooke et al. 204/58 3,073,765 1/1963 Adams 204/140 3,072,546 l/l963 Wruch 204/58 2,760,925 8/1956 Bryant 204/58 2,115,339 4/1938 Mason 204/58 3,400,057 9/1968 Coates et al. 204/33 OTHER PUBLICATIONS Anodizing of Al Alloys-Hardcoating by Spencer, Metal Finishing, 11/68, pages 58-68.

Primary ExaminerJohn H. Mack Assistant Examiner-R. L. Andrews Att0rneyH. Ross Workman 57 ABSTRACT A process for slating a curvilinear workpiece by electrolytically depositing aluminum oxide on the surface of the workpiece using a temperature controlled sulfuric acid bath containing a high concentration of aluminum. The process produces a craze-free, slightly abrasive surface useful for erasably receiving chalk marks. This process is particularly useful in forming world globes which may be used with chalk for educational and illustrative purposes and then easily erased.

9 Claims, 1 Drawing Figure ELECTROLYTIC PROCESS FOR SLATING A CURVILINEAR ALUMINUM WORKPIECE BACKGROUND' 1. Field of the Invention This invention relates to a process for slating aluminum and more particularly to a process for slating a curvilinear aluminum workpiece to make an improved craze-free surface for erasably receiving chalk marks.

The Prior Art Conventional blackboards have for a long time been used to receive chalk marks and the like. Historically, chalkboards or blackboards of fine quality must have a texture which is sufficiently coarse to cause the chalk to adhere to the surface and at the same time not so coarse that the chalk cannot be removed easily with an eraser. If the surface is too smooth, the chalk will not adhere and no marks would be visible on the chalkboard. On the contrary, if the surface is too rough or irregular, the chalk marks cannot be easily removed.

While a number of conventional techniques for making acceptable flat blackborad or chalkboard surfaces are known, the preparation of a curved or curvilinear chalkboard surface has been found extremely difficult. For example, in the manufacture of world globes, it is sometimes desirable to form the exterior globe surface of a chalkboard-type material so that chalk marks can be placed on the globe for instructional and illustrative purposes. However, when the curvilinear surface representing the exterior of the world globe is slated so as to have chalk-receiving characteristics, the surface becomes crazed or cracked. Crazing is the non-uniform cracking of a surface and is particularly a problem which occurs in curvilinear surfaces. After the surface has become crazed, removing chalk marks or other foreign material becomes very difficult if not impossible.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION The present invention provides a novel process by which an aluminum workpiece having a curvilinear surface is prepared so that the curvilinear surface'presents a craze-free chalk-receiving surface which can be completely and easily erased after use.

Accordingly, it is a primary object of the present invention to provide a novel process for treating a curvilinear aluminum surface to receive chalk.

It is another object of the present invention to provide an improved process for slating an aluminum workpiece so that the workpiece will readily accept chalk markings which can be easily erased thereafter.

These and other features and objects of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a pictorial flow diagram schematically illustrating sequential steps of one presently preferred process embodiment of the invention.

DETAILED DESCRIPTION OF THEPREFER RED EMBODIMENT The process which is the present invention has been found useful with any curvilinear: aluminum workpiece. However, to facilitate description of the process, the preparation of a slated world globe will be described.

of conventional hemisphere forming techniques and may be of any suitable size. It has been found that hemispheres having diameters of between six and twenty-four inches make convenient sized globes. While it may be desirable to bond or otherwise fasten hemispheres together at this point to form a spherical globe, it has been found more convenient to deal directly with hemispheres until the slating process is completed.

After the hemispheres have been formed, frequently serious surface irregularities exist. Accordingly, it is often desirable to use a polishing or grinding wheel 14 to remove the surface irregularities. Clearly, if no surface irregularities exist, the polishing or grinding step is unnecessary.

After the polished hemisphere 12 has been ground, the convex surface 16 is roughened essentially uniformly over the surface 16. The roughening is important so that when the slating process is completed, the texture of surface 16 will be sufficiently coarse that marks are easily made thereon. If the surface 16 is not roughened, at the conclusion of the slating process the surface may be too smooth to receive chalk marks. It has been found according to this presently preferred embodiment of the invention that a surface variation of between 20 and micro-inches is satisfactory to develop an improved chalk-receiving surface after slating.

The roughening process can be accomplished by blasting the surface 16 with a fine grit 18. Alternatively, chemical etching techniques and/or mechanical abrading can be used to achieve the desired roughening. Care should be taken to insure that the surface 16 is not overly coarse so that excess chalk is used and erasing becomes very difficult.

The hemispheres 16 thus prepared are next hard anodized. Anodizing means the electrolytic formation of aluminum oxide on the surface of the aluminum workpiece. The conditions under which the hard anodizing takes place are important to insure the proper slating on the curvilinar surface 16. An electrolytic container A 20 is provided which, when filled with an electrolytic medium 22 forms a bath for the hemisphere 12. The electrolytic medium 22 is preferably a strong sulfuric acid solution combined with a high concentration of aluminum. A sulfuric acid concentration of between 200 and 300 grams/liter has been found adequate when combined with approximately 20 grams/liter of aluminum. It has been found that where substantially less than 20 grams of aluminum are used, the resulting slated surface crazes over the curvilinear surface. While the specific mechanism resulting in increased crazing is not known, it is presently believed that the reduced aluminum content results in a more dense rigid surface coating having reduced elasticity. As a result, it is believed that the curvilinear configuration is more susceptible to crazing.

When the aluminum content approaches and exceeds 20 grams/liter, the slated surface has been found softer and more porous and crazing is substantially reduced if not eliminated. It is believed that the reduced crazing is a result of greater elasticity in the surface.

As illustrated in the drawing, the aluminum work piece 12 is electrically connected to the positive pole of a power source 24 so that a charge differential exists between the workpiece 12 and the bath 22. For example, it has been found advantageous to maintain a constant electrical current between the bath 22 and the workpiece 12 and to maintain that current, the voltage must be increased to compensate for increasing resistance in the electrolyte medium. To maintain a constant current of 36 amps/sq. ft. of workpiece surface, the voltage is varied between and 50 volts.

It is presently preferred that electrolysis be performed with the bath temperature below room temperature and preferably between 20 and 40 F. The temperature of the medium 22 may be reduced below room temperature, e.g. to 20 to 40 F by any suitable conventional means, a common refrigeration circuit 26 being illustrated in the drawing. It should be appreciated that any suitable heat exchange means could be used to maintain the temperature of the acid bath medium 22 in the range of about 20 to 40 F. The workpiece 12 is preferably hard anodized in the described apparatus until a coating of aluminum oxide has developed on the curvilinear surface 16 preferably to a thickness of between 0.001 and 0.006 inches. Of course, other thicknesses can be used depending upon the size of the surface variations formed in the curvilinear surface 16 at the toughening step.

After the hemisphere 12 has been anodized, if desired, it may be etched or a coloring agent may be applied to the curvilinear surface 16 of the aluminum so as to form a grid, outline of continents or the like. Clearly, where curvilinear surfaces other than world globes are used, any suitable marking could be placed on the anodized surface.

When the workpiece 12 is removed from the electrolytic bath, the workpiece is washed by spraying water 28 from a suitable nozzle 30 over the hemisphere. It has been found most advantageous to maintain the temperature of the water 28 so as not to exceed 70 F and after the workpiece has been thoroughly rinsed, it is air dried or dried in a conventional drier. workpiece 12 may then be bonded or otherwise rigidly secured to a similariy treated substantially identical hemisphere so as to form a globe, The globe may then be mounted upon a suitable globe stand for use.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

What is claimed and desired to be secured by United States Letters Patent is:

l. A process for slating a curvilinear aluminum workpiece comprising the steps of:

preparing the curvilinear surface of the workpiece so that a generaliy uniformly roughened surface resuits;

providing an electrolytic bath of strong sulfuric acid and an aluminum concentration in the sulfuric acid on the order of about 20 grams/liter; adjusting the temperature of the electrolytic bath to substantially below room temperature; and

immersing the curvilinear surface in the electrolytic bath and electrolytically forming aluminum oxide on the curvilinear surface.

2. A process for slating a curvilinear aluminum workpiece as defined in claim l wherein said preparing step comprises removing surface irregularities by polishing the curvilinear surface and thereafter treating the curvilinear surface so that it is generally uniformly roughened.

3. A process for slating a curvilinear aluminum workpiece as defined in claim 2 wherein said treating step comprises blasting the workpiece with a fine grit.

4. A process for slating a curvilinear aluminum workpiece as defined in claim 2 wherein said treating step comprises chemically etching the curvilinear surfacev 5. A process for slating a curvilinear aluminum workpiece as defined in claim 2 wherein said treating step comprises mechanically abrading the curvilinear surface.

6. A process for slating a curvilinear aluminum workpiece as defined in claim 1 wherein said adjusting step comprises refrigerating the electrolytic bath to a temperature of on the order of about 20 to 40 F.

7. A process for slating a curvilinear aluminum work piece as defined in claim 1 wherein said electrolytically forming step comprises oxidizing the aluminum to aluminum oxide on the curvilinear surface to a thickness of between 0.001 and 0.006 inches.

8. A process for slating a curvilinear aluminum workpiece as defined in claim 1 further comprising washing the electrolytically treated aluminum workpiece in water having a temperature not exceeding F and thereafter drying the workpiece.

9. A process for slating a curvilinear aluminum workpiece comprising the steps of:

obtaining a curvilinear aluminum workpiece;

polishing the surface to remove irregularities;

abrading the surface to form generally uniformly roughened characteristics;

preparing a sulfuric acid electroiytic bath having an aluminum concentration not less than 20 grams! liter; reducing the temperature of the bath to the range between 20 and 40 F;

immersing the workpiece and electrically charging the immersed workpiece with respect to the acid bath;

forming an aluminum oxide veneer upon the surface of the workpiece corresponding in thickness to the surface variation introduced by the abrading step; removing the workpiece from the acid bath; and washing the excess acid solution from the workpiece surface with water at a temperature of about 70 F.

i 4 t i 

2. A process for slating a curvilinear aluminum workpiece as defined in claim 1 wherein said preparing step comprises removing surface irregularities by polishing the curvilinear surface and thereafter treating the curvilinear surface so that it is generally uniformly roughened.
 3. A process for slating a curvilinear aluminum workpiece as defined in claim 2 wherein said treating step comprises blasting the workpiece with a fine grit.
 4. A process for slating a curvilinear aluminum workpiece as defined in claim 2 wherein said treating step comprises chemically etcHing the curvilinear surface.
 5. A process for slating a curvilinear aluminum workpiece as defined in claim 2 wherein said treating step comprises mechanically abrading the curvilinear surface.
 6. A process for slating a curvilinear aluminum workpiece as defined in claim 1 wherein said adjusting step comprises refrigerating the electrolytic bath to a temperature of on the order of about 20* to 40* F.
 7. A process for slating a curvilinear aluminum workpiece as defined in claim 1 wherein said electrolytically forming step comprises oxidizing the aluminum to aluminum oxide on the curvilinear surface to a thickness of between 0.001 and 0.006 inches.
 8. A process for slating a curvilinear aluminum workpiece as defined in claim 1 further comprising washing the electrolytically treated aluminum workpiece in water having a temperature not exceeding 70* F and thereafter drying the workpiece.
 9. A process for slating a curvilinear aluminum workpiece comprising the steps of: obtaining a curvilinear aluminum workpiece; polishing the surface to remove irregularities; abrading the surface to form generally uniformly roughened characteristics; preparing a sulfuric acid electrolytic bath having an aluminum concentration not less than 20 grams/liter; reducing the temperature of the bath to the range between 20* and 40* F; immersing the workpiece and electrically charging the immersed workpiece with respect to the acid bath; forming an aluminum oxide veneer upon the surface of the workpiece corresponding in thickness to the surface variation introduced by the abrading step; removing the workpiece from the acid bath; and washing the excess acid solution from the workpiece surface with water at a temperature of about 70* F. 